Franz Sigel (November 18, 1824 - August 21, 1902) was a German military officer and immigrant to the United States who was a teacher, newspaperman, politician, and served as a Union general in the American Civil War.

Sigel was born in Sinsheim, Germany. He graduated from Karlsruhe Military Academy in 1843 and was commissioned a lieutenant in the Baden Army. He got to know the revolutionaries Friedrich Hecker and Gustav von Struve and became associated with the revolutionary movement. He was wounded in a duel in 1847. The same year he retired from the army to begin law school studies in Heidelberg. After organizing a revolutionary free corps in Mannheim and later in the Seekreis county, he soon became a leader of the Baden revolutionary forces (with the rank of colonel) in the 1848 Revolution, being one of the few revolutionaries with military command experience. In April 1848, he led the "Sigel-Zug", recruiting a militia of more than 4,000 volunteers to lead a siege against the city of Freiburg. His army was annihilated on April 23, 1848 by the better-equipped and more experienced Prussian and Württemberg troops. After Prussia suppressed the revolution, he fled to Switzerland and then to England. Sigel emigrated to the United States in 1852, like many other German "Forty-Eighters".

Sigel taught in the New York City public schools and served in the state militia. In 1857 he became a professor at the German-American Institute in St. Louis. He was elected director of the St. Louis public schools in 1860. He was influential in the Missouri emigrant community and attracted Germans to the Union and anti-slavery causes when he openly supported them in 1861.

At the start of the war. Sigel recruited and organized an expedition to southwest Missouri and fought the Battle of Carthage, defeating 8,000 Confederates with only 800 of his own men. He was commissioned colonel of the 3rd Missouri Infantry on May 4, 1861. President Abraham Lincoln was actively seeking the support of anti-slavery, Unionist immigrants. Sigel was a good candidate to advance this plan and he was promoted to brigadier general two weeks later.

Sigel served under Nathaniel Lyon in the capture of the Confederate Camp Jackson in St. Louis and at the Battle of Wilson's Creek, where his command was routed. His finest performance came on March 8, 1862, at the Battle of Pea Ridge where he commanded two divisions and personally directed the Union artillery in the defeat of Major General Earl Van Dorn.

Sigel was promoted to major general on March 21, 1862. He served as a division commander in the Shenandoah Valley and fought unsuccessfully against Thomas J. "Stonewall" Jackson, who managed to outwit and defeat the larger Union force in a number of small engagements. He commanded the I Corps in John Pope's Army of Virginia at the Second Battle of Bull Run, another Union defeat, where he was wounded in the hand.

Over the winter of 1862-1863 Sigel commanded the XI Corps, consisting primarily of German immigrant soldiers in the Army of the Potomac. During this period, the corps saw no action; it stayed in reserve during the Battle of Fredericksburg. Sigel had developed a reputation as an inept general, but his ability to recruit and motivate German immigrants kept him alive in a politically sensitive position. Many of these soldiers could speak little English beyond "I fights mit Sigel", which was their proud slogan. They were quite disgruntled when Sigel left the corps in February, 1863, and he was replaced by Oliver O. Howard, who had no immigrant affinities. Fortunately for Sigel, the two black marks in the XI Corps' reputationChancellorsville and Gettysburgwould occur after he was relieved.

The reason for Sigel's relief is unclear. Some accounts cite failing health; others that he expressed his displeasure at the small size of his corps and asked to be relieved. General-in-chief Henry W. Halleck detested Sigel and managed to keep him relegated to light duty in eastern Pennsylvania until March, 1864. President Lincoln, needing political assistance in his quest for renomination, directed Secretary of War Edwin M. Stanton to place Sigel in command of the new Department of West Virginia.

In his new command, Sigel opened the Valley Campaigns of 1864, launching an invasion of the Shenandoah Valley. He was soundly defeated by John C. Breckenridge at the Battle of New Market, on May 15, 1864, which was particularly embarrassing due to the prominent role young cadets from the Virginia Military Institute played in his defeat. In July he fought Jubal A. Early at Harpers Ferry, but soon afterwards was relieved of his command for "lack of aggression" and replaced by David Hunter.

Sigel resigned his commission on May 4, 1865, and worked as a journalist in Baltimore, and as a newspaper editor in New York City. He filled a variety of political positions there, both as a Democrat and a Republican. In 1887, President Grover Cleveland appointed him pension agent for the city of New York. Franz Sigel died in New York in 1902 and is buried there in Woodlawn Cemetery.